| Reliable and accurate information on strength, failure mode, ductility and energy absorption capacity is required for the design of reinforced and prestressed concrete structures such as nuclear containment structures, reactor vessels, and for the development of new types of building construction such as coupled shear-wall frame system and shock absorbing first story concept, particularly for seismic loading conditions. If the basic constitutive relationships of the two major components (steel and concrete) of reinforced and prestressed concrete are known, then it would be possible using a computerized mathematical model to calculate ductility and other parameters for a wide variety of situations and combinations.; The first objective of this investigation was to obtain accurate and reproducible complete stress-strain curves of unconfined and confined concrete subjected to uniaxial monotonic and cyclic compressive loads. These curves were obtained for (a)two types of concrete (normal and lightweight aggregate concrete); (b)varying compressive strength (3,000 - 12,000 psi); (c)different amounts of lateral reinforcement ((rho)(,s) = 0.5 to 3.2 percent); (d)various yield strength of lateral reinforcement (60 (LESSTHEQ) f(,y) (LESSTHEQ) 208 psi); and (e)different strain rates (32 <(' )(epsilon)(' )< 30,000 microstrain/sec.). Prior to systematically obtaining the stress-strain curves, the effect of the testing parameters (method of obtaining the descending portion of the stress-strain curve, effect of size, shape of the specimen, effect of age at testing) and methods of measuring (gage length effects for strain measurements) were also carefully studied.; The second objective of this investigation was to develop a constitutive law under multiaxial compressive loadings, for predicting the complete (ascending and descending portions) stress-strain curves. A simple experimental technique (concrete confined in steel tube) was developed to obtain the post peak behavior under cylindrical triaxial compressive loadings. The post peak behavior predictions of the multiaxial constitutive law were calibrated from results of present work. Based on the proposed multiaxial constitutive law, a model for hoop confined concrete was developed. The model is sensitive to plain concrete strength, spacing and stress-strain curve of confining steel. Theoretical investigation also included the formulation of nonlinear finite element model (based on the proposed multiaxial law) to simulate the response of confined concrete. |
